Heretofore, laser light has been distinguished from light coming from other sources such as sun beams, lightnings, detonation light phenomena and so forth, in that the pulse rise time has been electronically measured. It is known that light pulses in a pulse sequence or pulse train come from a laser light source if the individual pulses have a very short rise time. Thus, only that radiation is interpreted as coming from a laser source which has shorter pulse rise times than a given threshold rise time value. This approach, however, is applicable only to pulse type laser sources. The approach is not applicable to lasers radiating on a continuous wave basis.